1. Field of the Invention
The present invention relates to bearings including rolling bearing and slider bearing, in particular, suitable for an apparatus driven by a high speed revolution with high quality precision, low vibration noise and low shock, and the method for manufacturing the same.
2. Related Art
Recently, for instance, in a spindle motor such as used for a memory apparatus in computer of magnetic type or optical type, due to a minute dimension change of bearing mechanism due to thermal expansion has become deteriorated in rotation precision to not disregarding extent.
Further, depending on kind of appliance, a revolution vibration to be generated at the bearing portion and a revolution noise coming from this vibration have become a big problem.
In addition, due to the miniaturization of appliances, there have been such problems as, since bearings to be used have been miniaturized too, an impact extent to be received by elements of bearing has become large, rolling elements or rolling surfaces of the rolling elements are easily damaged.
Also, the conventional bearings have been made, almost, of metals such as bearing steel and stainless steel, therefore, a thermal expansion coefficient has become relatively high and the effective decrease of the thermal expansion coefficient by a little variation of composite component is recognized to be extremely small, so that, against a deterioration of revolution precision due to the above minute change of size, an effective countermeasure has not found.
Further, since the generation of the above revolution vibration has been caused by a surface coarsening due to the wearing of the rolling surface in roller bearings and the bearing surface of sliding bearings and the engagement of different materials, the decrease of the surface coarsening becomes possible by increasing the hardness of the rolling surface or the bearing surface, however, concerning the above bearings made of metals there is a limitation for a high leveled hardening and it has been in a difficult situation to solve the generation of the revolution vibration and the sound derived from such vibration. Further, although the above the rolling surface and the bearing surface are finished by polishing, an abnormal surface layer (surface-softening layer) too influences the surface by causing to make the surface coarsened, which causes it more difficult to solve the problem of the revolution vibration.
Further, although the damages on the rolling element and rolling surfaces generated due to the increase of the impact because of miniaturization of appliances are to be related with the buckling strength, as to the above metal made bearings, since there is an limitation concerning the increase of the buckling strength, its solution has been in a difficult situation.
The present invention has been made to solve the various problems concerning the property of the material, and is to provide a bearing to cope effectively not only with the deterioration of revolution vibration due to the thermal expansion but also the generation of vibration noise due to the surface coarsening and the impact due to the miniaturization, and a method for manufacturing such bearings.
Bearings relating to the present invention are not limited to the type of rolling bearing or sliding bearing, and in the case where it is structured as a rolling bearing, whole of inner and outer rings or at least surface layer portion including rolling surface is formed with polycrystalline glass, on the other hand in case where it is structured as a sliding bearing, whole of a bearing body which receives as shaft or a surface layer or at least including bearing surface and the whole of the shaft or at least a surface portion to be received by the bearing body are formed with a polycrystalline glass.
Here, when forming as a rolling bearing, whole of rolling element (ball, roller) or its surface layer may be formed with a polycrystalline glass.
And as a sliding bearing, there is a liquid circulating bearing and an air circulating bearing and the present invention may include such bearings.
In the bearings of the present invention, the above glass may be of any type of glass if it is able to be crystalized, and for example such as a silicate glass, a borosilicate glass and a phosphate glass can be used. However, of these glasses, the silicate glass is preferable from the view point of superiority in mechanical strength and heat resistance. In this case, as silicate glass, a high silicate glass (quartz crystal), a soda-lime glass, an aluminosilicate glass, a borosilicate glass and alkali silicate glass. In such silicate glass, after being formed, it is crystalized by a heat treatment, and not only a coefficient of thermal expansion becomes small but also a hardness become higher, in addition, a mechanical strength, a heat resistance and an anti-corrosion will be increased.
In manufacturing the above bearing, when forming whole of the elements such as inner ring, outer ring, rolling element, bearing body using a molten glass, after forming a heat treatment may be carried out for crystalizing, on the other hand, in case where it is constructed as a sliding bearing, when only the surface layer of the above elements is to be formed with glass, after a base body of each element is made of a metal, a glass layer may be laminated on the surface of the base body, after that a heat treatment for crystalizing is carried out.